1. Polyploidy

2. Polyploidy in plants
Polyploidy is very common in plants, especially in angiosperms.
30% to 70% of angiosperms may be polyploid.
Chromosome content of most plant groups suggests that the basic angiosperm genome consists of the genes on 7–11 chromosomes.

3. Polyploidy in crop plants
Domestic wheat, with 42 chromosomes, is probably hexaploid (6n)
The ancestral haploid number (n) was 7.
Species of coffee plant with 22, 44, 66, and 88 chromosomes are known.
This suggests that the ancestral condition was a plant with a haploid (n) number of 11 and a diploid (2n) number of 22, from which evolved the different polyploid descendants.

4. Ploidy levels in other crops
Plant
Probable ancestral haploid number
Chromosome number
Ploidy level
domestic oat 7 42 6n
peanut 10 40 4n
sugar cane 80 8n
banana 11
22,33
2n,3n
white potato 12 48
tobacco
cotton 13 52
apple 17
34,51

5. Polyploidy and speciation
When a newly-arisen tetraploid (4n) plant tries to breed with its ancestral species, triploid offspring are formed.
These are sterile because they cannot form gametes with a balanced assortment of chromosomes.
However, the tetraploid plants can breed with each other. So in one generation, a new species has been formed.
Polyploidy even allows the formation of new species derived from different ancestors.

6. Polyploidy in Brassica hybrids
Three species in the mustard family appear to have arisen by hybridization and polyploidy from three other ancestral species:
B. oleracea x B. nigra → B. carinata Cabbage, etc Black mustard Abyssinian mustard
B. oleracea x B. campestris → B. napus Cabbage, etc Turnips Rutabaga
B. nigra x B. campestris → B. juncea Black mustard Turnips Leaf mustard

7. Triangle of U (the “U” is from a mis-translation of Woo Jang-Choon, who discovered the relationship)

8. Polyploidy in animals Polyploidy is much rarer in animals
Examples: some insects, fishes, amphibians, reptiles.
Until recently, no polyploid mammal was known
A polyploid (4n=102) rat has been found in Argentina.
Polyploid cells are larger than diploid ones
More DNA in their nucleus.